1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus. More specifically, the invention relates to an ink-jet printing apparatus to be employed in a facsimile apparatus, a printer, a copy machine and so forth.
2. Description of Related Art
As such type of apparatus, an ink-jet printing apparatus as employed in a facsimile apparatus will be discussed with reference to FIG. 1.
A plurality of printing papers P are stacked in a cassette 51 and are fed one by one by means of a feeder roller 52 into a transporting path formed by a transporting roller 53. The printing paper P is further transported to a printing portion B by rotation of the transporting roller 53. The printing portion B has an ink-jet head in which are arranged a plurality of (64, for example) ejection openings in transporting direction (auxiliary scanning direction) of the printing paper P and which is provided for scanning in a direction perpendicular to the transporting direction (primary scanning direction) so that ink is ejected toward the printing paper P so as to print image and so forth. The printed printing paper P is transported to a discharge portion along a lower guide 55 by a discharge roller pair 54 arranged at downstream side of the printing portion B in the transporting path and discharged to a discharge paper stacker 58 as discharge stacking portion by means of a discharge roller 56 and a discharge roll 57 to be stacked therein.
Various systems for performing printing on printing media, such as paper, OHP sheet and so forth have been known. Amongst those, an ink-jet printing system to be employed in the conventional apparatus set forth above is to directly eject into toward the printing medium. Such ink-jet system is advantageous in relatively low running cost and low level of noise to be generated associated with a printing operation. On the other hand, in the ink-jet system, it becomes necessary to quickly detect running out of the ink or ejection failure for preventing printing failure from occurring.
In the ink-jet printing apparatus, as a method for detecting faulty condition of ejection, such as running out of the ink, ejection failure due to plugging, clogging and so forth, there has been known a technology for passing the ejected ink droplet between a light emitting element and a photo-sensing element of a transmission type photosensor and detecting ejection failure based on whether the light between the elements is interrupted or not.
In one example of construction of the above-mentioned transmission type photosensor, a lens is integrally formed on a light emitting surface of the light emitting element. By this, substantially parallel light is projected toward the photo-sensing element. On the other hand, in a photo-sensing surface of the photo-sensing element, an aperture in the order of 0.7 mm.times.0.7 mm is formed on a light axis by a molding member. By this, in the overall range between photo-sensing and light emitting, detecting range is limited at approximately 0.7 mm in height and approximately 0.7 mm in width. Further, the light emitting element and the photo-sensing element are arranged so that a light axis extending therebetween is in parallel to ejection opening array of the ink-jet head and intersects with a flying path of the ejected ink droplet. Also, a distance between the light emitting element and the photo-sensing element is set to be wider than a range of the ejection opening array. By this, all of the ink droplets ejected from respective ejection openings of the ink-jet head may pass through the detection range between the light emitting element and the photo-sensing element. Thus, when the ink ejection is performed normally and the ink droplet passes the detection range, the ink droplet interrupts the light beam from the light emitting side to reduce the amount of light reaching the photo-sensing side to cause variation of output of the photo-sensing element. The ejected ink droplet is in the form of a fine liquid droplet having a diameter less than or equal to 50 Am. Therefore, normally, single ink droplet ejected from single ejection opening may not interrupt the light emitted from the light emitting side completely. Instead, light interruption ratio is gradually increased depending upon number of ejection openings ejecting ink. Accordingly, when the output of the transmission type photosensor varies in a magnitude greater than or equal to a given amount, ink ejection is judged as normal. Conversely, when the variation magnitude of the transmission type photosensor is less than or equal to the given amount, failure of ink ejection can be detected.
When ejection failure is detected, the facsimile apparatus prohibits reception of subsequent printing operation command until operation for recovery of ejection is performed and inhibits reception of data, or accumulates received data in a memory to previously prevent the data from being lost. It has been known that a detection operation of ejection failure performed after completion of printing for each page is effective.
The technology for detecting ejection failure may perform detection without adding any special parts for the ink-jet head. Therefore, it can be employed as effective means for detection of ejection failure.
However, in the above-described prior art, the number of ejection openings normally performing ejection and variation amount of the output of the photosensor are substantially proportional. On the other hand, output of the transmission type photosensor normally fluctuates approximately 20% at maximum due to fluctuation of performance of the light emitting element and the photo-sensing element, fluctuation of play in assembling the elements and so forth. Therefore, there can not be detected an occurrence of ejection failure even when partial ejection failure of a plurality of ejection openings occurs.
For example, in the case that an ink-jet head having 64 ejection openings and the photosensor which causes output higher than that set with respect to actual light receiving amount, are used, even if 12 ejection openings corresponding to less than 20% of the number of overall ejection openings causes ejection failure, lowering of the sensor output corresponding to ejection failure can not be detected accurately, and therefore it was impossible to detect the occurrence of partial ejection failure of these ejection openings. In such case, printing can not only be performed in the condition causing ejection failure to cause degradation of quality of the printed product, but printing is performed in a condition that a part of received data are not printed and a problem that it needs to request retransmission of the data is raised especially on the facsimile apparatus.
Further, magnitude of fluctuation of the photosensor output is determined with taking a cost as important factor. Therefore, if steps for selecting elements constituting the photosensor and adjusting the photosensor are to be neglected for lowering of cost, the above-described fluctuation is increased to make a condition regarding the photosensor worse. Therefore, the construction for detecting ejection failure in the prior art serves as hazard for cost down.
On the other hand, even if partial failure of the ejection openings is detected by making fluctuation of sensor output smaller in the construction for detecting ejection failure in the prior art, since failure detecting is done as detection of ejection failure of the overall ink-jet head, such detection may cause prohibiting of reception of the subsequent printing request.
It is possible that 16 ejection openings, which is one fourth of 64 ejection openings, have ejection failure and thus 48 ejection openings operate normally. In such case, despite the fact that printing can be performed by employing normally operating 48 ejection openings, printing operation is inhibited and inhibit reception of the receiving data to perform operation accumulating the received data in the memory or so forth. Particularly, the facsimile apparatus is frequently used for automatic reception without monitoring by an operator. Therefore, even when the reception data is stored in the memory under printing inhibited condition, it may occur that the facsimile apparatus must be situated into the reception inhibiting state when an amount of data more than capacity of the memory is received, due to limited capacity of the memory to cause significant inconvenience of the facsimile apparatus.